NCERT Solutions for Class 9 Science Chapter 8

Class 9 Science – Physics -Motion

Important Questions with answers

Question 1:
A train travels 100 m long moving on a straight level track passes a pole in 5 s. Find (a) the speed of the train (b) the time it will take to cross a bridge 500m long.

Answer 1:
(a) 20 m/s
(b) 30 s

Question 2:
A car travelling at 36 km/h speeds upto 72 km/h in 5 seconds. What is its acceleration? If the same car stops in 20 seconds, what is the retardation?

Answer 2:
2 m/s² ; -1 m/s²

Question 3:
Usha swims in 90 m long pool. She covers 180 m in one minute by swimming from one end to the other and back along the same straight path. Find the average speed and average velocity of usha.

Answer 3:
3 ms^-1 ; zero

Question 4:
Ahmed is moving in his car with a velocity of 45 km/h. How much distance will he cover (a) in one minute and (b) in one second?

Answer 4:
750 m ; 12.5 m

Question 5:
A train starting from rest attains a velocity of 72 km h^-1 in 5 minutes. Assuming that the acceleration is uniform, find (i) the acceleration and (ii) the distance travelled by the train for attaining this velocity.

Answer 5:
1/15 m/s² ; 3 km

Question 6:
A body starts to slide over a horizontal surface with an initial velocity of 0.5 m/s. Due to friction, its velocity decreases at the rate of 0.05 m/s². How much time will it takes for the body to stop?

Answer 6:
10 seconds

Question 7:
A car accelerates uniformly from 18 km/h to 36 km h/ in 5 second. Calculate (i) the acceleration and (ii) the distance covered by the car in that time.

Answer 7:
1 m/s² ; 37∙5 m

Question 8:
What does the odometer of an automobile measure?

Answer 8:
The odometer of an automobile measures the distance travelled by the vehicle.

Question 9:
What is the nature of the distance-time graph for uniform and non-uniform motion of an object?

Answer 9:
When the motion is uniform, the distance-time graph is a straight line with some slope.
When the motion is non-uniform, the distance time graph is not a straight line. It can be any curve.

Question 10:
What is locomotion?

Answer 10:
Locomotion is the ability of an animal to move its whole body from place to place without any external forces.

Question 11:
What type of motion of tips of second’s hand of a watch? Is it uniform or accelerated?

Answer 11:
The motion of the tip of second’s hand of a watch is not a uniform motion. It is accelerated motion due to change in the direction of motion.

Question 12:
Define speed and velocity. What are their SI units?

Answer 12:
Speed: Speed of a body is defined as the distance travelled by the body in unit time.
Velocity: Velocity of a body is the distance travelled by the body in unit time in a given direction.
The SI unit is meter/second.